The present invention relates generally to rotors, and more particularly to damping unwanted rotor vibrations.
Rotors are the rotatable portions of rotary machines, and rotary machines include, without limitation, X-ray tubes, a centrifugal compressor, a steam turbine (including a turbine portion thereof) used by a power utility company, and a gas turbine (including a compressor portion or a turbine portion thereof) used as an aircraft engine or used by a power utility company.
It is known to dampen vibrations of a rotor of an aircraft gas turbine engine by installing a split-ring damper in a damper-ring groove of the rotor. The rotor may include rotor blades attached to, and extending radially-outward from, a shaft, or the rotor may be a monolithic blisk having shaft and blade portions. The damper-ring groove is a circumferential, radially-inward-facing groove on the shaft or shaft-portion of the rotor with the groove being coaxially aligned with the longitudinal axis of the rotor. To prevent longitudinal motion of the split-ring damper, the groove may have two longitudinally-spaced-apart side walls or, in the case of a tapered shaft, the groove may have a single side wall. The split-ring damper is a metallic ring having a single, radially-aligned through-cut. The weight, flexibility (Young""s modulus), and surface friction characteristics of the split-ring damper are chosen (by experiment, computer analysis, and/or closed-form equations) to provide the most damping for a particular amplitude of one rotor vibrational mode of one natural vibrational frequency which typically corresponds to an expected maximum amplitude of a dominant vibrational mode of an excitation frequency which is closest to steady-state rotor operation. The split-ring design of the damper provides ease of installation in the damper-ring groove and allows frictional damping (by microslippage) between the outer circumferential surface of the split-ring damper and the rotor. Such damping is less effective or ineffective to dampen vibrations below the expected maximum amplitude, such as small-amplitude vibrations which may lead to fatigue failure of the rotor. What is needed is improved rotor damping.
In a first embodiment of the invention, apparatus for damping a rotor includes at least a first and a second damper ring wherein the outer diameter of the second damper ring is generally equal to the inner diameter of the first damper ring. In a second embodiment, a rotor assembly includes a rotor having a damper-ring groove and includes the previously-described at least first and second damper rings positioned in the damper-ring groove. A first expression of a method of the invention obtains and positions the previously-described at least first and second damper rings in the damper-ring groove of a rotor.
In a third embodiment of the invention, apparatus includes a damper-ring assembly having an inner damper ring, an outer damper ring, and a viscoelastic layer positioned radially between and bonded to the inner and outer damper rings. In a fourth embodiment, a rotor assembly includes a rotor having a damper-ring groove and includes the previously-described damper-ring assembly positioned in the damper-ring groove.
In a fifth embodiment of the invention, a rotor assembly includes a rotor having a damper-ring groove and includes a damper-ring assembly positioned in the damper-ring groove, wherein the damper-ring assembly has an outer damper ring and has a viscoelastic layer positioned radially between and bonded to the outer damper ring and the rotor.
In a sixth embodiment of the invention, a damper ring includes a generally ring-shaped housing having a hollow portion and includes particulate matter located within the hollow portion of the housing. In a seventh embodiment, a rotor assembly includes a rotor having a damper-ring groove and includes the previously-mentioned damper ring disposed in the damper-ring groove.
In an eighth embodiment of the invention, apparatus includes single-wire strands twisted together to define a cable, wherein the cable has a shape of a split ring. In a ninth embodiment, a rotor assembly includes a rotor having a damper-ring groove and includes the previously-described cable positioned in the damper-ring groove.
Several benefits and advantages are derived from the invention. The known single-ring design of the prior art provides frictional damping between the outer circumferential surface of the ring and the rotor only for large-amplitude vibrations. In an at-least-two-ring embodiment of the invention, the outer circumferential surface of the inner ring and the inner circumferential surface of the outer ring undergo microslippage and hence frictional damping in response to small-amplitude vibrations, and, for large-amplitude vibrations, there is added thereto the frictional damping of the outer circumferential surface of the outer ring with the rotor. Engineering analysis shows that dividing one ring into two or more concentric rings (of the same total weight as the one ring) provides more damping over a larger range of vibrational amplitudes than does the one ring. In a viscoelastic-layer embodiment of the invention, the viscoelastic layer provides damping in the form of viscous damping for smaller-amplitude vibrations, and, for larger-amplitude vibrations, there is added thereto the frictional damping of ring-rotor contact or ring-ring contact. In a hollow-damping-ring embodiment of the invention, the particulate matter provides particulate frictional damping for smaller-amplitude vibrations, and, for larger-amplitude vibrations, there is added thereto the frictional damping of the ring""s housing with the rotor. In a cable embodiment of the invention, the twisted single-wire strands provide frictional damping between strands for smaller-amplitude vibrations, and, for larger-amplitude vibrations, there is added thereto the frictional damping of the cable with the rotor.